Lessons From The Past: ALS Resistance

The start of 2011 marked two decades since the first ALS-resistant weeds — kochia and Russian thistle — were documented in Montana. “The first resistant weeds were discovered in my area,” says Brad Birch, owner of Dry Fork Ag, Ledger, MT. “Everybody had been using ALS chemistry, when they first began seeing reduced performance, they weren’t sure what was going on, but then a bioassay confirmed that the kochia was resistant.”

Ed Davis, research agronomist at Montana State University, explains that adoption of ALS chemistry was so quick and widespread because it controlled the state’s big three weeds of kochia, Russian thistle and wild buckwheat. “Close to 90% of our growers relied on ALS herbicides, and they worked really well for about four years,’ says Davis. “But then, we got a few complaints about not getting complete control. About two years later, there was widespread non-performance in the field. Within five years, we had lost most of our ALS products.”

Eventually, he says, this same situation began playing out in neighboring states such as North Dakota. Ultimately, growers were forced to replace ALS herbicides with older chemistries such as 2,4-D.

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